In a V-block refractometer, a sample is placed on a V-shaped groove formed on a V-block prism, and the sample is irradiated with measurement light through the V-block prism. The measurement light passing through the sample is detected by a detector, whereby a refractive index of the sample can be measured (see Patent Document 1 below, for example).
FIG. 5 is a schematic plan view illustrating an example of a configuration of a conventional V-block refractometer. The refractometer includes, in addition to the above V-block prism 101 and the detector 102, a light source unit 103 that emits measurement light, a first optical system 104 that guides the measurement light from the light source unit 103 to the V-block prism 101, and a second optical system 105 that guides the measurement light passing through the V-block prism 101 to the detector 102.
The light source unit 103 includes a mirror 132 that is rotatable about a rotation shaft 131 extending in the perpendicular direction (front-to-back direction of the sheet of FIG. 5), and a plurality of light sources 133 that is arranged in an arc about the rotation shaft 131 and capable of emitting measurement light having different wavelengths. With this, the measurement light from the light source 133 according to the rotation position of the mirror 132 can be reflected on the mirror 132 in the horizontal direction, and guided toward the first optical system 104.
The first optical system 104 includes a lens 141, mirrors 142, 143, and 144, an interference filter 145, a slit 146, a collimator lens 147, and the like. Measurement light passing through the lens 141 and reflected on the mirrors 142 and 143 is incident on the interference filter 145 selected according to the type of the light sources 133, and only the measurement light (monochromatic light) having a specific wavelength passes through the interference filter 145. The measurement light passing through the interference filter 145 is reflected on the mirror 144, passes through the slit 146, is converted into parallel light by the collimator lens 147, and emitted to the sample through the V-block prism 101.
The second optical system 105 includes mirrors 151 and 152, a telemeter lens 153, a beam splitter 154, and the like. The second optical system 105 is fixed to a circular disc 107 mounted to a rotation shaft 161 of a motor 106. Specifically, the mirrors 151 and 152 and the telemeter lens 153 are arranged parallel to the rotation shaft 161 at an eccentric position relative to the rotation shaft 161, and the mirror 152 and the beam splitter 154 are fixed to the circular disc 107 so as to be arranged vertically in a row relative to the rotation shaft 161.
Measurement light passing through the beam splitter 154 is incident on the detector 102 fixed to the circular disc 107. On the other hand, the measurement light reflected on the beam splitter 154 is reflected on a mirror 108, and then, passes through a lens 109 to be guided toward an eyepiece unit (not illustrated) where the state of the measurement light can visually be recognized. The beam splitter 154 and the mirror 108 are provided on the rotation shaft 161. When the position of the V-block prism 101 is adjusted, an auto collimation prism 110 can be interposed on the optical path between the beam splitter 154 and the mirror 108.
With the above configuration, measurement light from the V-block prism 101 can be received at different angles with the rotation of the motor 106, and can be guided to the detector 102. The measurement light from the V-block prism 101 at each rotation angle is detected by the detector 102 by rotating the motor 106. With this, the rotation angle at which the detection intensity becomes the highest can be specified, and the refractive index of the sample can be measured based on this rotation angle and the refractive index of the V-block prism 101.